At the beginning of this reaction, 1 molecule of 'elongating pre-rRNA transcript', and 1 molecule of 'NTP' are present. At the end of this reaction, 1 molecule of 'elongating pre-rRNA transcript' is present.

This reaction takes place in the 'nucleolus' and is mediated by the 'DNA-directed RNA polymerase activity' of 'RNA Polymerase I promoter escape complex'.